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Chapter 162 Resources for the Hematologist e9

Immunoglobulin E
Summary points • Important in immune response to deep parasitic (nematode) infections
• Important mediator of allergic response; level often elevated in patients with bronchial asthma or atopic dermatitis
Methodology Nephelometry, immunoassay
Specimen requirements Plain or serum separator tube
Indications Suspected allergic disease; monitoring allergic bronchopulmonary aspergillosis
Reference range Table 162.22
Interpretation • Low levels in hypogammaglobulinemia and selective IgE deficiency
• Elevated levels in allergic diseases, deep parasitic infections, malignancy, drug allergy, immune deficiency, some
infections and inflammatory disorders; rarely monoclonal IgE gammopathies
• IgE measurement has limited value in diagnosing atopy given large overlap between atopic and nonatopic individuals
• Normal levels do not exclude allergy
Related tests IgA, IgG
Interfering substances Lipemia, other causes of extreme turbidity, microbial contamination
References Bacharier LB, Geha RS: Regulation of IgE synthesis: The molecular basis and implications for clinical modulation. Allergy
Asthma Proc 20:1, 1999.
Hamilton RG, Adkinson NF Jr: Clinical laboratory assessment of IgE-dependent hypersensitivity. J Allergy Clin Immunol
111:S687, 2003.

Ig, Immunoglobulin.

Immunoglobulin G
Summary points • Largest fraction of serum immunoglobulins; important component of secondary humoral immunity
• Elevation seen in monoclonal gammopathies and many polyclonal infectious or inflammatory conditions
Methodology Nephelometry
Specimen requirements Plain or serum separator tube
Indications Suspected immune deficiency (primary or secondary) or monoclonal gammopathy, assess response to immunization or
recent or previous infection when antigen-specific IgM and IgG are tested
Reference range Table 162.23
Interpretation • Polyclonal elevations seen in hypergammaglobulinemia, chronic liver disease, collagen vascular diseases, autoimmune
diseases, some infections
• Monoclonal elevations seen in monoclonal gammopathies (plasma cell dyscrasias); confirmed by serum protein
electrophoresis with immunofixation
• Decreased in immune deficiencies, hypogammaglobulinemia, states of protein loss (protein-losing enteropathy,
nephrotic syndrome), some malignancies, medications
• Normal IgG levels do not exclude humoral immunodeficiency—further functional studies (assessment of antibody
response post vaccine administration) and/or IgG subclasses may be required if high degree of clinical suspicion
• Reference intervals may vary with methodology and patient ethnicity
Related tests IgM, IgA, lymphocyte subsets, serum protein electrophoresis with immunofixation
Interfering substances Lipemia, other causes of severe turbidity, microbial contamination
Ig, Immunoglobulin.

Immunoglobulin G Subclasses
Summary points • IgG subclass deficiencies are uncommon but may be associated with recurrent bacterial infections
• Total serum IgG may be normal, even with a subclass deficiency
Methodology Nephelometry
Specimen requirements Plain or serum separator tube
Indications Suspected humoral or combined immune deficiency with normal total serum IgG levels, recurrent respiratory or sinus
infections. Testing IgG subclasses has a limited role for assessment of antibody-mediated immune function in patients
with recurrent sinusitis and respiratory infections
Reference range Table 162.24
Interpretation • Decreased levels in hypogammaglobulinemia
• Most frequent abnormality: IgG2 deficiency or combined IgG2-IgG4 deficiency. IgG2 deficiency may be associated with
IgA deficiency in patients with chronic respiratory infection
• Decreased IgG3 levels may be seen in primary immunodeficiencies (Wiskott-Aldrich syndrome) and type 1 diabetes
mellitus
• 70% of serum IgG is IgG1—selective IgG1 deficiency is rare
• Significance of decreased IgG4 in absence of IgG2 deficiency uncertain
Related tests IgG, IgM, IgA
Interfering substances Lipemia, other causes of severe turbidity, microbial contamination
Reference Maguire G: Are there any clinical indications for measuring IgG subclasses? Ann Clin Biochem 39:374, 2002.

Ig, Immunoglobulin.